The Summerston distance slab from the western end of the Roman Antonine Wall in Scotland was once brightly painted in warning reds, yellow and white.Credit: Hunterian Museum/University of Glasgow

Ancient Romans used blood red, bright yellow and stunning white paints to illustrate dire warnings on the wall that separated them from the rebellious tribespeople of Scotland, a new study shows.

The painted warnings — including Roman eagles with blood-stained beaks, and the slain and decapitated bodies of the defeated victims of the victorious Roman legions — were shown alongside Latin inscriptions on carved stone slabs placed along a Roman rampart in Scotland.

Archaeologist Louisa Campbell from the University of Glasgow says the carved and painted stone slabs would have served as "Roman propaganda" to local tribespeople north of the Antonine Wall, a fortified wall built across Scotland by the Roman legions during the reign of the emperor Antoninus Pius in the second century A.D.

Although the stone slabs are plain gray today, Campbell’s research shows that they were once brightly colored with naturally made paints, including red and yellow ochre, a red mineral called realgar, a red plant dye known as madder, a bright yellow mineral called orpiment and white lead.

The reds, in particular, were used to paint details, such as the cloaks of Roman soldiers, and to signify the bloody end in store for enemies of the Roman Empire. "The scenes depicted by the iconography demonstrate the power and might of Rome in a highly graphic manner," Campbell told Live Science in an email.

The stone slabs, placed at intervals along the Antonine Wall, would have promoted the idea of Roman control of the region, both to the Roman armies and visitors from the empire, as well as to the indigenous peoples who lived around and north of the wall, she noted.

The stones were "a very visible message to the indigenous peoples of those regions that Rome is a powerful empire that will not tolerate any challenge to her authority," Campbell said.

Warning stones

Campbell studied all 19 of the known Roman "distance stones" found along the Antonine Wall, a fortification built by the Roman military to extend their control north of Hadrian's Wall, which was constructed about 60 miles (96 kilometers) to the south after A.D. 122, during the reign of the emperor Hadrian.

The Antonine Wall wasn't as long as Hadrian's 84-mile-long (135 km) wall, but it was still substantial, running almost 40 miles (64 km), from east to west between two deep river estuaries, or "firths," on opposite sides of Scotland — from the Firth of Forth, today just north of the city of Edinburgh, to the Firth of Clyde, just a few miles west of Glasgow.

Campbell's research included the two most famous stones from the Antonine Wall: the Summerston slab, which was found on a farm near Glasgow around 1694, and the Bridgeness Slab, discovered in 1868 near the town of Falkirk, at the eastern end of the Antonine Wall.

The Bridgeness stone also showed a decapitated warrior in the midst of battle. Both ends of the warrior's severed neck were once painted bright red to symbolize blood, Campbell's research revealed. Ancient artists may have also highlighted a carved Roman eagle on the Summerston slab with blood-red paint, she added.

"I would suggest the red on the beak of the eagle (the symbol of Rome and her legions) symbolizes Rome feasting off the flesh of her enemies," Campbell wrote in the email.

The Roman eagle on the Summerston slab also rests on the mythical figure of a capricorn, or sea-goat – the symbol of Rome's Second Legion, who defended the wall in that area and who had dedicated the stone to the emperor Antoninus Pius, she said.

Rome's final frontier

Despite its powerful propaganda messages, the Antonine Wall was occupied by Roman defenders only until A.D. 161, when Marcus Aurelius became emperor, and for a few years, from A.D. 208 to 211, during the reign of Septimius Severus.

Archaeologists don't agree why the Romans failed to establish the Antonine Wall as the northernmost border of the empire, but in the early third century they abandoned it and withdrew to Hadrian's Wall.

While many stone ruins are still visible along Hadrian's Wall, many of the remains of the earth and wooden ramparts of the Antonine Wall are now hard to distinguish from the surrounding countryside.

But new archaeological research is helping scientists map the ancient wall. Patricia Weeks, an archaeologist with the government heritage agency Historic Environment Scotland (HES), told Live Science that a survey using lidar technology, which uses laser light to map almost invisible distortions on the ground, along the full length of the Antonine Wall.

Data from this survey had been used as part of a study of the Antonine Wall by Nick Hannon, an archaeologist at Canterbury Christ Church University in the England, to explore relationships between different sites on the wall, and to try to identify any overlooked elements, such as additional small forts, Weeks told Live Science in an email.

The data from the survey and other work by archaeologists is being used to engage the public. Detailed 3D scans of artifacts from the Antonine Wall, including some of the distance slabs studied by Campbell, have been made public by HES at the Sketchfab 3D website.

The survey data and 3D artifact scans have also been incorporated in an educational game about a Roman fort along the wall, and in an interactive augmented-reality tour of the Antonine Wall, to help visitors to the region better understand and visualize the ancient structures, Weeks said.